Across Africa, juju men like Mr. Ambani do a brisk business in the soccer season trying to influence the action on the field. They cast spells on opposing teams. They throw magic powder on the goals to keep the ball out. They prescribe special diets for the players to propel them to victory.

''Juju works,'' insists the 74-year-old Mr. Ambani, a 40-year veteran of the trade who is a ''team adviser'' for several Kenyan soccer clubs. He pulled out a Skippy peanut butter jar full of small seashells, threw them on a table and analyzed the pattern, which -- to him -- represented the future without his intervention. He also rubbed a secret green powder on his palms, which he said helped him with the exercise.

To trip up opposing players, he puts a piece of cloth bearing their names into a clay pot. He adds chicken and porcupine blood and a special blend of herbs that has been handed down to him from juju elders. He plugs the holes in the pot with the horns of a goat and heats up the concoction on his stove.

Superstition runs deep in Africa, and sports-related juju reflects that. Many spectators watch the bouncing ball at soccer matches but keep one eye on suspicious individuals on the sidelines who might be trying to put a hex on the action.

Even a stray dog can cause controversy. At one recent professional match in Kenya, a dog urinated on the field during play, causing an uproar among juju believers and accusations that a team manager was trying to sway the result unfairly.

So widespread is this specialized juju, especially in West Africa, that the Confederation of African Football slapped a ban on soccer-related witchcraft before the African Cup of Nations in Mali this year. ''We are no more willing to see witch doctors on the pitch than cannibals at the concession stands,'' the confederation said.

Mr. Ambani, who operates out of this sprawling slum on the outskirts of Nairobi, has no doubt that the four teams from sub-Saharan Africa who competed in this year's World Cup -- Senegal, which made it to the second round, and South Africa, Cameroon and Nigeria, which did not -- had hometown juju men working on their behalf.

Although he claims to be able to know the outcome of matches and tournaments ahead of time, Mr. Ambani still watches games and says he enjoys doing so because he has not predicted every last kick.

Although most Africans consider soccer sorcery to be foolishness, there are still those who believe that intense training is only part of the recipe for soccer success. ''To depart for an international competition without consulting or including sorcerers is akin to going to an exam without a pencil,'' African Soccer magazine said recently.

Kenya is not now and never has been in the running for the World Cup but that has nothing to do with the abilities of the country's juju men, Mr. Ambani and other local believers say. Players must follow the directions of the juju men explicitly -- and truly believe in them -- if the score and the season are to come out right.

Back in 1974, the Leopards of Zaire took a team of witch doctors to the team's World Cup matches. Unfortunately, something went awry. The club fell to Scotland and Brazil in the opening matches and was then walloped 9 to 1 by Yugoslavia.

Perhaps an opponent had put an even stronger curse on the Zaire team, Mr. Ambani said.

When England racked up a long losing streak in World Cup competitions, another Kenya-based juju man wrote to the team manager in advance of the 1990 World Cup offering his services.

''Your team has fared disastrously since winning the World Cup in 1966,'' Abubakar Shariff Omar wrote. ''You may not know the reason but it is because they lack the magic charm that has helped other teams.'' (England did not take up the offer).

The one-room wooden shack from which Mr. Ambani operates is crowded with a double bed, a gas stove and several shelves full of potions. There are glass jars that look like something from a chemist's lab, as well as makeshift containers that used to hold peanut butter or vegetable oil.

Mr. Ambani acknowledges that he is not a rich man. Like so much else in the world, good juju depends on money, and Africans are often not willing to dig deep enough to bring about victories.

''It's all about money,'' he said, describing the price for his services as anything from a few dollars to a few thousand dollars, depending on the complexity of the task. ''It takes time for me to do this work. I sometimes have to sleep outside without clothes to bring a victory. I need to be paid.''

Mr. Ambani played soccer himself as a younger man; his two sons also play, but neither has yet followed in his footsteps when it comes to juju.

Paul Ambani, 17, is a believer though. He allows his father to rub his legs with a special liquid before his youth league matches to fend off injuries. He also accepts his father's explanation that juju works only at the professional level. Paul Ambani's team had five victories, one loss and three draws last season, a good record for a normal boy but average for the son of a juju man.

Photos: Jackson Ambani, a witch doctor specializing in soccer, predicts the future for a young player and draws attention when sitting outside a video center. Across Africa, juju men do a brisk business in the soccer season. (Photographs by Francesco Broli for The New York Times) Map of Kenya highlighting Kangemi: The witch doctor Jackson Ambani hangs his shingle in Kangemi.